A host of water soluble polymers, both synthetic and naturally occurring, have found extensive use in a variety of fields. Illustrative synthetic polymers include olefin oxide polymers such as poly(ethylene oxide) and copolymers of ethylene oxide with other lower olefin oxides such as propylene oxide, butylene oxide and the like, water soluble vinyl addition polymers such as the various acrylamide polymers, polyvinyl alcohol and many others. Naturally occurring water soluble polymers include a wide variety of plant-derived gums, resins, polysaccarides and the like.
Solutions of the polymers typically exhibit flocculating and thickening properties. Illustrative industrial applications include use as a flocculating agent in the clarification of aqueous solutions and suspensions as, for example, sewage and industrial wastes and in the secondary recovery of petroleum through water flooding. Certain of the high molecular weigh polymers, particularly high molecular weight poly(ethylene oxide), can reduce the turbulent frictional drag of water flowing through a conduit by as much as 80% at concentrations of a few parts per million. That effect is especially useful in fire fighting and similar applications wherein it is desired to deliver a large volume of water through a restricted conduit at a high rate.
It can be quite difficult to obtain a uniform water solution of many of the highly soluble polymers, particularly if the particles of the polymer are very small. As the polymer particles start to dissolve, a very concentrated and sticky solution forms around each particle. Contact of the partially dissolved particles, one with another, forms aggregates and lumps of polymer which resist dissolution. In almost all cases the simple addition of polymer particles to water, with or without stirring, results in agglomeration of the polymer particles into clumps which are then very difficult to dissolve.
A number of different approaches and techniques for dissolving water soluble polymers have been developed. For example, Union Carbide Corporation in its Brochure No. F-42933 entitled "How to Dissolve POLYOX Water Soluble Resins", describes three separate approaches or categories for the dissolving of poly(ethylene oxide) polymers. These are: 1. simple direct addition in water; 2. predispersion in water-miscible non-solvents; and 3. special mechanical methods to achieve dispersion with minimal shear.
Direct addition of powdered polymer to water requires stirring devices of proper design in order to obtain good dissolving. A paddle stirrer arranged to create a large vortex at a slow stirring rate is considered best for that use. High velocity stirring devices cannot be used effectively as the high shear produced by such devices causes extreme degradation of the polymers. The degradation effect is most severe with the higher molecular weight polymers.
Water-miscible non-solvents useful to predisperse poly(ethylene oxide) polymers for later dissolution include boiling water, concentrated salt or alkali solutions, and organic non-solvents. Poly(ethylene oxide) polymers are completely soluble in water until near the boiling point at which temperature they precipitate. Likewise, those polymers are insoluble in concentrated solutions of sodium hydroxide, sodium chloride, ammonium hydroxide and a variety of other salts. There are several water-miscible organic solvents in which poly(ethylene oxide) polymers are not soluble at room temperature. Those include, among others, anhydrous ethanol and isopropanol, certain glycols and acetone. After pre-dispersing the polymer particles in the non-solvent, water is added with mixing to form a solution.
A variety of mechanical devices have been developed for the batch and continuous dissolving of water soluble polymers. Apparatus specifically adapted for the dissolving of poly(ethylene oxide) polymers are illustrated by two patents to Harvey, et al, U.S. Pat. Nos. 3,129,064 and 3,147,955 and by another patent to Morse, et al, U.S. Pat. No. 3,606,093. The devices disclosed in those three patents disperse polymer particles onto a thin sheet of flowing water so as to avoid the agglomeration of the particles into gel lumps. Another mechanical device for dissolving polymers is illustrated in U.S. Pat. No. 4,846,582 to Davidsson. Polymer particles are introduced perpendicularly into a jet of water such that the particles are captured by the jet which is then projected against a surface causing the jet to change direction and break up into droplets. One more dissolving device is described in U.S. Pat. No. 4,537,513. Patentees first disperse polymer particles in a non-aqueous liquid and thereafter rapidly merge the polymer dispersion with a stream of water in an orifice mixer.
Yet another approach to dissolving water soluble polymers, specifically gels of polyacrylamide polymers, is described by Pogers in his U.S. Pat. No. 4,069,161. Pogers freezes the polymer gel and grinds it to form fine particles which are thereafter mixed with water. The frozen gel particles dissolve in the water as they thaw.
Finally, the Anderson patent, U.S. Pat. No. 3,624,019, discloses a technique for dissolving water soluble, vinyl addition polymers by first dispersing the polymers into a water-in-oil emulsion and then inverting the emulsion in water. Inversion of the emulsion causes the polymer to be released into the water to form a solution.
All of the prior art techniques for dissolving water soluble polymers require cumbersome apparatus or complicated techniques in order to obtain solutions. None of the methods or devices known in the prior art allows for the dissolving of polymers by simple addition of the polymer to water as one would do in the dissolving of salts and like compounds.
With this background, it can readily be appreciated that the formulation of water soluble polymers, particularly such polymers as poly(ethylene oxide) and polyacrylamides, in a manner which allows the preparation of aqueous polymer solutions by direct addition of the polymers to water provides an important advance in the art.